--- a/ChangeLog
+++ b/ChangeLog
@@ -9,6 +9,10 @@
  * Added the functions `encode()` and `get_serializer()` to the `genshi.output`
    module, which provide a lower-level API to the functionality previously only
    available through `Stream.render()` and `Stream.serialize()`.
+ * The `DocType` class now has a `get(name)` function that returns a `DOCTYPE`
+   tuple for a given string.
+ * Added frameset variants to the `DocType` constants for HTML 4.01 and XHTML
+   1.0.
 
 
 Version 0.4

--- a/genshi/output.py
+++ b/genshi/output.py
@@ -81,8 +81,14 @@
         'html', '-//W3C//DTD HTML 4.01 Transitional//EN',
         'http://www.w3.org/TR/html4/loose.dtd'
     )
+    HTML_FRAMESET = (
+        'html', '-//W3C//DTD HTML 4.01 Frameset//EN',
+        'http://www.w3.org/TR/html4/frameset.dtd'
+    )
     HTML = HTML_STRICT
 
+    HTML5 = ('html', None, None)
+
     XHTML_STRICT = (
         'html', '-//W3C//DTD XHTML 1.0 Strict//EN',
         'http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd'
@@ -91,9 +97,40 @@
         'html', '-//W3C//DTD XHTML 1.0 Transitional//EN',
         'http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd'
     )
+    XHTML_FRAMESET = (
+        'html', '-//W3C//DTD XHTML 1.0 Frameset//EN',
+        'http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd'
+    )
     XHTML = XHTML_STRICT
 
-    HTML5 = ('html', None, None)
+    def get(cls, name):
+        """Return the ``(name, pubid, sysid)`` tuple of the ``DOCTYPE``
+        declaration for the specified name.
+        
+        The following names are recognized in this version:
+         * "html" or "html-strict" for the HTML 4.01 strict DTD
+         * "html-transitional" for the HTML 4.01 transitional DTD
+         * "html-transitional" for the HTML 4.01 frameset DTD
+         * "html5" for the ``DOCTYPE`` proposed for HTML5
+         * "xhtml" or "xhtml-strict" for the XHTML 1.0 strict DTD
+         * "xhtml-transitional" for the XHTML 1.0 transitional DTD
+         * "xhtml-frameset" for the XHTML 1.0 frameset DTD
+        
+        :param name: the name of the ``DOCTYPE``
+        :return: the ``(name, pubid, sysid)`` tuple for the requested
+                 ``DOCTYPE``, or ``None`` if the name is not recognized
+        :since: version 0.4.1
+        """
+        return {
+            'html': cls.HTML, 'html-strict': cls.HTML_STRICT,
+            'html-transitional': DocType.HTML_TRANSITIONAL,
+            'html-frameset': DocType.HTML_FRAMESET,
+            'html5': cls.HTML5,
+            'xhtml': cls.XHTML, 'xhtml-strict': cls.XHTML_STRICT,
+            'xhtml-transitional': cls.XHTML_TRANSITIONAL,
+            'xhtml-frameset': cls.XHTML_FRAMESET,
+        }.get(name.lower())
+    get = classmethod(get)
 
 
 class XMLSerializer(object):

--- a/genshi/template/plugin.py
+++ b/genshi/template/plugin.py
@@ -30,7 +30,7 @@
 __docformat__ = 'restructuredtext en'
 
 
-class ConfigurationError(Exception):
+class ConfigurationError(ValueError):
     """Exception raised when invalid plugin options are encountered."""
 
 
@@ -111,23 +111,21 @@
     template_class = MarkupTemplate
     extension = '.html'
 
-    doctypes = {'html': DocType.HTML, 'html-strict': DocType.HTML_STRICT,
-                'html-transitional': DocType.HTML_TRANSITIONAL,
-                'html5': DocType.HTML5,
-                'xhtml': DocType.XHTML, 'xhtml-strict': DocType.XHTML_STRICT,
-                'xhtml-transitional': DocType.XHTML_TRANSITIONAL}
-
     def __init__(self, extra_vars_func=None, options=None):
         AbstractTemplateEnginePlugin.__init__(self, extra_vars_func, options)
 
-        doctype = self.options.get('genshi.default_doctype')
-        if doctype and doctype not in self.doctypes:
-            raise ConfigurationError('Unknown doctype "%s"' % doctype)
-        self.default_doctype = self.doctypes.get(doctype)
+        default_doctype = self.options.get('genshi.default_doctype')
+        if default_doctype:
+            doctype = DocType.get(default_doctype)
+            if doctype is None:
+                raise ConfigurationError('Unknown doctype %r' % default_doctype)
+            self.default_doctype = doctype
+        else:
+            self.default_doctype = None
 
-        format = self.options.get('genshi.default_format', 'html')
+        format = self.options.get('genshi.default_format', 'html').lower()
         if format not in ('html', 'xhtml', 'xml', 'text'):
-            raise ConfigurationError('Unknown output format "%s"' % format)
+            raise ConfigurationError('Unknown output format %r' % format)
         self.default_format = format
 
     def _get_render_options(self, format=None):